The invention relates to a system and method for the burn-in of electronic components such as semi-conductors and the like.
Integrated circuits (ICs), after manufacture and prior to use in a computer system, undergo a variety of tests to ensure they are defect free and will perform as intended. One of the tests conducted is known as burn-in.
Test systems for component testing are well known; for example, semi-conductor life tests in burn-in chambers are common. The process of burning-in typically consists of applying a load to the components being tested at elevated temperatures. This allows identification of weak or faulty components and thus procludes their ultimate use, such as in a computer system.
In addition to burn-in ovens or hot air ovens, other technologies used for this purpose are open loop conduction heating, such as hot plates and thermal probes and liquid bath systems.
The burn-in ovens are by far the most prevalent test device and method used. Second in importance are the liquid burn-in bath methods.
In order to apply a load to the components under test, driver electronics are used which must be isolated from the hot thermal environment of the high temperature oven or liquid bath. This means that the driver electronics must be some distance from the devices under test (DUTs) which compromises frequency limits. Further, DUT trays must be high temperature material which adds to the costs of the testing procedure. The burn-in ovens, or forced air systems, typically have plus or minus 3.degree. C. gradients throughout the chamber as required by MIL-STD-883. However, device heat dissipation makes determining the actual case temperatures (and therefore, junction temperatures) very difficult. Materials used in the chamber must be rated at the highest operating temperature, i.e. sockets, capacitors, resistors, connectors and PC board material. Semi-conductors cannot be used on the PC board above 75.degree. C. because of their unreliability at these temperatures. High frequency applications (approximately 5 mHz) require multi-layer polyimide, PCB's, mother boards, daughter boards and extender boards to be used. High pin count devices require very high I/O's through chamber walls or a compromise must be made. Further, clock cards outside the chamber driving long distances (typically as long as 30 inches) compromise the high frequency operation. In liquid bath systems, the problems are the same as the burn-in ovens. Further, they are more expensive to operate, more inconvenient to operate and clock circuits cannot be put in the bath.
Briefly, some of the common problems with current technology is that the driver electronics are remote from the DUTs. This affects signal quality, the maximum signal frequency that can be used and results in signal skew, cross talk and overshoot. The I/O through the oven walls is not especially suitable for high pin count VLSI components and there is a practical limit to the number of I/O's and the possibility of impairment of signal quality. The trays used in the ovens are expensive, high temperature material. Perhaps the most severe problem is that there are temperature variations throughout the oven due to flow dynamics and one is never really sure of the actual DUT junction temperature. Further, the large monolithic ovens are not amenable to small lot burn-in, independent temperature cycling or independent DUT cool down under bias.
It would be desirable to have the driver electronics as close as possible to the DUT, preferably located on the burn-in tray and to conduct the burn-in in ambient conditions. Most importantly, accurate independent temperature control of each DUT on a burn-in tray would be desirable.
Broadly the invention comprises a thermal control system for burn-in of DUTs which accurately and independently controls the device case temperature of each DUT with close-loop conductive heating and further includes over temperature protection, under temperature protection and junction temperature correction. Using a close-loop method of conductive heating for each DUT, the invention can heat the device case temperature to say 200.degree. C. at an accuracy of less than plus or minus 2.degree. C. The invention uses closed-loop sensors that read temperatures directly from the device case assuring that the DUT reaches the desired temperature at each DUT position. A conductive module which includes a heater and sensors engages the DUT. Therefore, a separate heat source services each position. Thermal control for each position is via a dedicated microprocessor with the processor set up in turn by a computer. With individual control, each position can be heated to different temperatures over different time intervals. The sensor which reads the temperature of the DUT is isolated from the heater which contacts the DUT. Therefore, the temperature reading is not influenced by the temeprature of the heater. Further, the sensor and heater are individually suspended whereby uniform engagement with the DUT is ensured.
In a preferred embodiment, the system is embodied in a tower-like structure where each position is located on the outer surface of the structure. The conductive module is secured to the outer surface of the tower, its heater and sensors extending outwardly. The DUT socket releasably engages the conductive module at the DUT position. Mother boards containing the DUT clock card with driver electronics are arrayed vertically in the tower in a wall-like configuration and communicate with lower horizontally-fixed backplanes secured in the tower. These backplanes distribute the DC voltages to the mother boards which in turn distribute the load to the DUT's. Thermal control boards communicate with upper backplanes, which backplanes are secured horizontally in the tower. These boards control the DUT device case temperature. The control board communicates with a microprocessor via the upper backplane.
The conductive modules are secured to the tower and pass through the mother board. The conductive modules are computer controlled by the thermal control boards. The DUT sockets frictionally engage the mother board and electrically communicate therewith. The DUT contacts a sensor on the conductive module. Because the driver electronics can be placed close to the DUT, the system provides signal quality greater than 40 mHz.